Several different processes for making alpha alumina are described in the prior art. For example, one known process is described in an article by Edward N. Lussky entitled "Experience with Operation of the Alcoa Fluid Flash Calciner", Light metals, pages 59-79 (1980). The present invention represents an improvement upon the process described by Lussky in the aforesaid article.
In accordance with the present invention, alpha alumina production is promoted by addition of alpha alumina promoter particles along with alumina hydrate seed material in a Bayer process precipitation. The precipitated alumina hydrate particles are then dried and calcined. Addition of promoter particles during the precipitation step promotes alpha alumina formation in the calcination step. When the promoter particles are added. alpha alumina is formed at a lower temperature and in smaller particle size than when no promoter is utilized.
It is a principal objective of the present invention to provide an economical process for production of alpha alumina particles which substantially avoids any need for boehmite formation at an intermediate stage.
A related objective of the invention is to provide a process for making smaller particles of alpha alumina than in prior art processes based upon flash calcination of gibbsite particles.
Another related objective of the invention is to provide a process for production of alpha alumina particles wherein gibbsite particles are calcined at a lower temperature than in prior art processes.
Additional objectives and advantages of the present invention will become apparent to persons skilled in the art from the following specification and claims.